Abstract: A radome with polarization conversion for high power radial spiral array antenna is designed. Three-layer dielectric substrate are used to sandwich double-layer metal meander line to form sealed and embedded structure. The power capacity can be improved by avoiding the contact between the metal and the air while the conversion between the circular polarization and the linear polarization is realized. The influence of each parameter of the embedded meander-line grid unit is analyzed, and the unit parameters are optimized. An embedded meander-line radome with polarization conversion is made and loaded into an X-band high power helical array antenna. The basic performance and power capacity of the antenna are analyzed. The simulation results show that the matching performance of the antenna is good, the axial ratio of the center frequency is changed from 1.16 dB to 40 dB, and the circular polarization is converted to linear polarization. Through preliminary analysis, the power capacity of the embedded radome with polarization conversion is 121 MW, and the high power application of the radome with polarization conversion is realized.